Optimus - Penn State College of Engineering · IS Code Description IS 875 (Part 1): 1987 Dead loads IS 875 (Part 2): 1987 Imposed loads IS 875 (Part 3): 1987 Wind loads. 3))))) 1

Punit G. Das | Structural Technical Report 2

October 12, 2012 The Optimus | India 1The

Opt

imus

Punit DasStructural OptionAdvisor Dr. Linda Hanagan

AE SENIOR THESIS 2012-13TECHNICAL REPORT 2

Signature Boutique Offices India

Table of ContentsExecutive Summary! 3

Building Introduction! 4

Structural System Overview ! 6

Foundations 6

Gravity Framing System 7

Lateral System 7Design Codes! 8

Materials! 10

Gravity Loads! 12

Pro-Con Study of Floor Systems! 15

Flat Slab with Drop Panels 16

Composite Floor Slab system 18

Steel metal deck and Joist System 20

Precast Double Tee Floor System 22Comparison table of Floor Systems! 24

Conclusion! 25

Appendix 1: Flat Slab! 26

Appendix 2: Composite! 31

Appendix 3: Steel Metal Decking! 38

Appendix 4: Precast Floor System! 44


October 12, 2012 The Optimus | India 2

Executive SummaryThe purpose of the report is to analyze and perform a pro-con study of the existing and alternative floor systems. This is achieved by doing a preliminary design of three alternative floor systems. The design is performed using loads common to a typical 27.6‘x27.6’ bay on a typical office floor. The 4 floor systems compared are:-

1. Flat slab with drop panels (existing)

2. Composite system

3. Steel decking with joists

4. Precast Double Tee

The 8” flat slab system with 4’6 x 4’6 drop panels is one of the top viable choices because it is cheaper and fits best with the construction methods in India. It also gives a higher desirable floor to ceiling height. However, one of the drawbacks is that its is the heaviest of the four systems. This system was checked for short and long term deflections and seem to conform with ACI Specifications.

A composite system is also equally a top viable choice among the three alternative systems. A 3” 3VLI concrete deck topped with 4.5” concrete on a W10x22 wide flange beam forms a fully composite section that sits on a fully composite W18x55 girder gives a depth that is slightly high as comparable to the flat slab. The system is lighter and is cheaper from the scenario of construction in US. However, this would get expensive if constructed in India. However, the slight higher price gives an efficient system over a flat slab.

The fastest to construct precast system was designed using service loads and using the Precast Concrete Institute Handbook. A double tee prestressed concrete slab that has 10’ wide flange and is 24” deep is a lighter but expensive choice over a flat slab system. Also, it gives a high depth which decreases floor to ceiling height.

The 3” 3C18 metal deck with 3” concrete topping on 24” joist is the least viable choice because it is expensive and gives a much high depth which is not architecturally acceptable. However, one of the great advantages of steel decking is that it is lighter resulting in a lighter building.



Building Introduction

The Optimus, is a new building coming up in the city of Bombay, the economic capital of India. In a city that thrives on all kinds of businesses from small scale to large corporate companies, The Optimus will be catering medium size companies to set up their offices close to the business district of the city. The location is highly mixed use, as it contains residential towers, large shopping malls, office buildings and factories. While the future of the location is going to be marked by tall skyscrapers soaring about 100 stories, The Optimus is designed to provide a much humble yet modern look to fit in the fabric of the city.



Optimus

Figure 1 Aerial map from Google.com showing the location of the building site.

The design of The Optimus in the interior and exterior is very functional as well as aesthetic. It makes an efficient use of space within tight boundaries of the site and provides spacious floor space to its inhabitants. To cater the requirements of the offices, it offers open and customizable floor space. The spacing of the structural and architectural elements offers flexible partitioning for office spaces. The building provides recreational facilities that include a gymnasium, roof garden, green balcony spaces at every floor and a garden at the lobby area. The 2 basements and first 3

levels are dedicated to parking with 5 level as garden, lobby and office. The

office spaces start from 6 to 16th story and 17th story contains a roof garden.

Just as the interior, the exterior of the building is efficient in utilizing the available resources at the same time maintaining its aesthetic qualities. The envelope of the building designed to fit the location which also becomes an architectural feature of the building. Three kinds of materials decorate the facade: metal, stone and plants. As the north facade of the building faces a tall residential tower, all the office space is moved to the south facade

and giving a better view of stone and green wall to the residents of the adjacent tower. The south facade is dominated by a bold and modern look with metal cladding and windows pushed inside to provide solar shading in the interior. The front facade that faces the main street shows a play of all materials on the facade: stone, metal and green wall giving a rich look

to the building front.

The structure of the building is something that complements the architectural beauty. A successful building is achieved when its structure and architecture integrate without compromise, and this applies to The Optimus. In order to provide the celebration of facade, open floor plan and efficient floor area, the structure plays a very significant role. All the columns in the floor area are pushed to the exterior so that interior is open and at the same time no column is visible in the exterior to provide different architectural features on the facade. In this way the structural system of building does not



Figure 2 Rendering showing roof garden

Figure 3 Rendering of the building entrance

Figure 4 Rendering of the building facade

compromise the architecture but celebrates it.

Structural System OverviewThe structural systems of The Optimus has been optimized to increase floor space area, to celebrate the architecture and decrease the overall cost of the building without compromising safety. In order to achieve these goals, concrete was chosen as a prime material to support the building. The properties of concrete allows fluidity in design, room for design changes during construction and makes the construction process cheaper by employing the ample of labour force available at a cheaper cost. All the structural systems from foundation to slabs come together to improve efficiency in design and safety.

FoundationsThe geotechnical investigation report was performed by Shekhar Vaishampayan Geotechnical Consultants Pvt. Ltd. and special care was taken to avoid disturbances to adjacent buildings as the site is tightly surrounded by factories and residential buildings. As the building has two basement floors, the geotechnical investigation included excavation qualities of the site. Besides excavation, the soils report consists of soil bearing capacity of the soil, water table information, properties of soils and rocks at different levels below ground.

8 boreholes were drilled and soil properties were analyzed in a lab. It was discovered that soil properties consisted of filled up soil, medium to stiff clay, weathered rock and highly to slightly weathered tuff. The minimum depth of excavation was determined to be 12.5 m / 41 feet below ground level. The basement raft was decided to be placed 10 m / 33 ft below ground level. The soils report explained that the soil and clay below ground would exert lateral pressures on the basement walls. To account for these lateral pressures, the reinforced concrete frame and the main structure of the building will internally support the basement



Figure 5 Boring test map on the building site.

walls. Therefore, the basement walls were designed for hydrostatic pressure as well as the earth pressure. The ground water table was determined to be present at a depth of 1.00 m / 3.3 ft below ground. This was a conservative figure chosen by the geotechnical consultant to account for the built of water pressures during heavy monsoon season in the city.

Gravity Framing SystemThe reinforced concrete framing system of The Optimus is developed to fit the different types of floor spaces from the basement to top floor. The column, beam and slab system is chosen to fit with the architecture of the building as well as to act as an architectural element.

Architecture and structural system integration is seen in the columns of the building that change its cross sectional properties and layout as the space progresses from basement to the top of the building. The columns from the basement to the level 5 are rectangular and oriented parallel to the parking spaces. These rectangular columns transition to circular and square columns in office spaces from level 5 to the top level. This transition is occurs with the use of transfer girders, columns brackets and adjustments to account for eccentricity in the columns. The columns sizes range from 1.5 ft to 3 ft in the weak axis and 1.5 ft to 7 ft in the strong axis direction. Circular columns range from 1.5 ft to 3 ft in diameter in the office areas. the building has a peculiar column with cross section of a parallelogram. This column is located at the entrance of the building and defines the corner of the building from the base to the top adding to the architecture.

The columns are tied together with beams, girders and mainly the flat slab system of the floor framing. The 8 - 12 in slabs connect to the columns with drop panels ranging about 2 in additional depth. Drop panels mainly exist at parking spaces and thin drops are added at slabs in office spaces. The slabs also create interaction between the columns and core walls of the building and help distributing gravity loads.

Lateral SystemThe wind and seismic forces are handled by the extensive shear walls that exist around the stairwells and elevator core. These reinforced concrete shear walls range from 8 in to 20 in thickness are designed to resist lateral and torsional forces due to wind and seismic loads. These walls span from basement to the top of the building and are connected using link beams. In N-S direction of the building, the shear wall and to some point the strong axis of the columns help in resisting the lateral forces. This is because width of the building is small in the N-S direction and strong axis of columns provide support to the shear walls through the connection with the slab. In the long side of the building i.e. the E-W direction the long and strong axis of the shear walls seem adequate to control drifts and resist forces in the E-W direction.



Design CodesAs the building is located in India, the Indian Standard (IS) code is used to design The Optimus. However, in this report the American codes are used for checks and analysis. This will provide a comparison between the two codes and also a look into the design from the perspective of the american rules.

• Minimum design loads for Buildings other than seismic loadsIS Code Description

IS 875 (Part 1): 1987 Dead loads IS 875 (Part 2): 1987 Imposed loadsIS 875 (Part 3): 1987 Wind loadsIS 875 (Part 5): 1987 Special loads and load combinations

• Seismic Provisions for buildingsIS Code Description

IS 1893: 2002 Criteria for earthquake resistance design of structure

IS 4326: 1993 Earthquake resistant design and Construction of Buildings - Code of Practice

IS 13920: 1993 Ductile Detailing of Reinforced concrete Structures subjected for Seismic Forces - Code of Practice

• Building code requirements for Structural Concrete:IS Code Description

IS 456: 2000 Plain and Reinforced Concrete - Code of practice

SP 16 Structural use of concrete. Design charts for singly reinforced beams, doubly reinforced beams and columns.

SP 34 Handbook on Concrete Reinforcement & Detailing

IS 1904 Indian Standard Code of practice for design and construction foundations in Soil: General Requirements



IS Code Description

IS 2950 Indian Standard Code of Practice for Design and Construction of Raft Foundation (Part –1)

IS 2974 Code of practice for design & construction of machine foundation

IS 2911 Code of practice for design & construction of Pile foundation (Part I 1o IV)

• Building code used for Structural SteelIS Code Description

IS 800: 1984 Code of practice for general construction in Steel

• Design codes to be used for Tech 1 American codes to analyze the existing conditions.

American Code Description

ACI 318-11 Concrete Design CodeASCE 7-10 Minimum design loads for

Buildings and Structures for Dead, Live, Wind and Seismic loads.



MaterialsMaterials used on this project help achieve efficiency in the structural system. In vertical structural the strength of the materials increases as the required strength of the member increases. This helps in improving efficiency by increasing material strength instead of increasing the size of the member.

Use of the material Indian Code American Code

Material Equivalent Material

Raft and pile foundations

M40 5000 psi

PCC M15 3000 psislabs and beams M40 5000 psi

Perimeter basement wall except Grid A

M40 5000 psi

Perimeter basement wall on Grid A

M60 7000 psi

Walls, Columns and Link beams from

foundation for 5th floor

M60 7000 psi

Walls, Columns and Link beams from 5th

floor to above

M40 5000 psi



ConcreteConcreteConcreteConcreteConcreteConcrete

Indian CodeIndian CodeIndian Code American CodeAmerican CodeAmerican Code

Concrete Grade

f’c (psi) Ec (ksi) Equivalent Concrete type

f’c Ec = 57000√f’c (ksi)

M60 7000 5614.3 High strength concrete 28 days

7000 psi 4768.9

M40 4700 4584.3 Ordinary ready mix 5000 psi 4030.5M15 1750 2807.2 Ordinary ready mix 3000 psi 3122.01

fck is 28 compressive strength for 150mmx150mm cube.

Poission’s ratio = 0.2

Coefficient of thermal expansion = 9.9x10-0.6 per deg C.







f’c - specified compressive strength of concrete.

Coefficient of thermal expansion = 5.5x10-6 per deg F.

Poissions ratio = 0.2



Poissions ratio = 0.2



Poissions ratio = 0.2ReinforcementReinforcementReinforcementReinforcementReinforcementReinforcement

According to IS: 1786 Fe 415 (Fy = 415 MPa/ 60 ksi) or Fe 500 (Fy = 500 MPa) steel bars are used.



According to ASTM A615, deformed and plain carbon steel bars are used with Fy = 60 ksi. According to ASTM A615, deformed and plain carbon steel bars are used with Fy = 60 ksi. According to ASTM A615, deformed and plain carbon steel bars are used with Fy = 60 ksi.



Gravity LoadsThe dead, superimposed and live loads used on the project are used from the IS Code whereas the report uses ASCE 7-10 provisions to calculate live loads. The superimposed dead loads are used the same that is on the project because they are loads from actual materials like floor finishes used on the project. The difference in live loads and calculation procedures like Live load reduction will cause difference in analysis results. However, the assumption is that indian code will give more conservative results because it accounts for contingencies in construction and materials used on the project. The tables below shows the difference in loading values between the IS code and ASCE 7-10 provisions.

• Typical Dead LoadsIS Code (kN/ m3) ACI 318-11 / ASCE 7-10 (lb / ft3)

Normal weight Concrete 25.00 150Floor finishes / Plasters 20.00 140

Loading Area Type of Load IS Code (kN/ m2)ACI 318-11 / ASCE 7-10

(lb / ft2)

Parking Space and Drive-way

Superimposed Dead Load 1.75 36.6

Parking Space and Drive-way

Live Load (vehicles) 2.50 non-reducible 40 non-reducibleParking Space and Drive-way

Live Load (fire truck over ground floor) 15.00 non-reducible

300 (AASHTO LRFD Bridge design

standards) - non-reducible

Covered Entryway over ground floor

Superimposed Dead Load 7.25 151.4Covered Entryway

over ground floorLive Load 4.00 100

Entrance Lobby, Elevator lobbies

Superimposed Dead Load 2.00 41.8Entrance Lobby,

Elevator lobbiesLive Load 3.00 100

Mechanical Floor Superimposed Dead Load

2.00 41.8Mechanical Floor

Live Load 7.50 Non-reducible 150 non-reducible

Electrical room over ground floor

Superimposed Dead Load 2.00 41.8Electrical room

over ground floorLive Load 13.50 non-reducible 282 non-reducible




(lb / ft2)

StairsSuperimposed Dead

Load 1.50 31.33Stairs

Live Load 3.00 100

Toilet roomsSuperimposed Dead

Load 4.50 94Toilet rooms

Live Load 2.00 40

Typical OfficeSuperimposed Dead

Load 3.00 62.7Typical Office

Live Load 4.00 100

Retail over ground floor

Superimposed Dead Load 4.575 95.6Retail over ground

floorLive Load 4.00 100

Eatery and UtilitySuperimposed Dead

Load 3.00 62.7Eatery and Utility

Live Load 5.00 100

Outdoor Utility over Level 105, 107 and similar

Superimposed Dead Load 5.625 117.5Outdoor Utility

over Level 105, 107 and similar

Live Load 5.00 100

Planted Terrace Superimposed Dead Load 12.50 261.1Planted Terrace

Live Load 3.00 100

Amenity / Fitness Center

Superimposed Dead Load 3.50 73.10Amenity / Fitness

CenterLive Load 5.00 100

Water tank over level 119

Superimposed Dead Load 3.50 73.1Water tank over

level 119Live Load 35 non-reducible 731 non-reducible

Electrical Panel room at ground

floor

Superimposed Dead Load 2.00 41.8Electrical Panel

room at ground floor

Live Load 13.50 non-reducible 282 non-reducible

RoofSuperimposed Dead

Load 5.50 114.9Roof

Live Load 3.00 Non-reducible 100 non-reducible




(lb / ft2)

Peripheral loads Superimposed Dead line load over wall

surface0.75 15.7

• Live load reduction According to IS 875 (part 2) - 1987, section 3.2, live load had been reduced.

IS CodeIS Code ASCE 7-10

Walls, columns, piers, their supports and foundation:

Walls, columns, piers, their supports and foundation:

Reduction in live loads is carried out as per the provision in ASCE 7-10 Section 4.7.2/

Number of floors supported

% reduction in total live load


1

2

3

4

5 to 10

over 10

0

10

20

30

40

50 Reduction in live loads is carried out as per the provision in ASCE 7-10 Section 4.7.2/

Beams, girders and trussesBeams, girders and trusses


Supported Area % reduction in total live load


less than 50m2

50m2 to 100 m2

100m2 to 150 m2

150m2 to 200 m2

200m2 to 250m2

Over 250 m2

0

5

10

15

20

25




Pro-Con Study of Floor SystemsThe main purpose of the report is to analyze the existing floor system and comparing it with 3 alternative systems. The report analyses the existing flat slabs system with a composite floor system, metal deck on joist and joist girders and precast double tee slabs.

A typical bay of an office floor is taken into consideration for analyses. The bay size is 27.6’ x 27.6’ and loads considered are 100 psf live load, 62.7 psd superimposed dead load and dead load of the system in consideration. The live load is a conservative value because the floor is an open floor plan and the renters have the flexibility to design the partitioning, corridors, pantry rooms according to their choice. The 62.7 psf superimposed dead load comes from the floor finishes that might be used by the future tenant of the office space. Its only in the steel metal decking system where the superimposed dead load is reduced to minimize deflections due to service loads.

Using the typical bay and loads, all the floor system were compared based on its weight, cost, constructability and impact on structural and architectural systems. As the building is located in India, the cost and constructability are compared based on the conditions in India. The cost of labor is cheap which makes a concrete system cheaper; however, steel construction is expensive as steel buildings are rarely preferred and skilled labor for steel construction is expensive.



Typical 27.6’ x 27.6’ bay

Fig. 6: Typical Office Floor Plan. Highlighted portion shows typical bay to be analyzed

Flat Slab with Drop PanelsAll the typical office floors of The Optimus are designed as two-way flat slabs with drop panels. The slab is 8” thick typical size of drop panel is 4’6”x4’6” x 8”. The primary purpose of the drop panel is to reduce deflections and punching shear in 27’6” long spanning slab. A secondary purpose is to help the slab increase the moment carrying capacity. However, this is majorly carried by the top and bottom reinforcement. The drop panels are not reinforced which proves that its does not provide much help to moment carrying capacity of the slab.

All the floors are constructed using the M40 concrete which is equivalent to 5000psi concrete available in USA. In most of the floor area 8” slab is used. Slab depths have been increased to 11.5” in fire areas also called refuge areas where there is a higher chance of live load occurring during an event like fire. Because mechanical loads are approximated and not acquired from the mechanical consultant, the utility areas which house mechanical equipment have thicker slabs for a more conservative design.

The reinforcing in the flat slab consists of #3 bottom bars spaced at 11in and a combination of #3 and #14 top bars spaced at 6” to 11” distances. The columns are spaced at 27.6’ in both direction to produce typical square bays for office spaces. The slab is design to carry partition loads and live loads from office spaces as well as facade loads at the perimeter of slabs.

• GeneralThe slab weights 98.5 pounds per square foot (psf) which is serving as a reference to compare the weights of the other alternative systems. The RS Means CostWorks website, gives latest cost information about each material and process carried out in the construction of the system. The flat plate system costs $14.8 per square feet according to RS Means and its National USA cost data. However, in the context of the construction practices in India this price would decrease because of cheap labor and less skill being in concrete construction. This would be the cheapest system among the other three systems. Also, concrete is a more widespread used product over Steel in India which makes it cheaper.



Fig. 7: Flat slab bay

Fig. 8: Column Strip

Fig. 9: Middle Strip

• ArchitecturalIn India, architecturally it is preferred to use a false ceiling and hide the mechanical system above the false ceiling. Hence, Flat slab is one of the widely used floor systems as it provides a floor to ceiling height from 9’ to 15’ which is a preferred height in office spaces. A flat slab system improves the visual quality of the building form the exterior because it does not contain any beams or undulations in the ceiling surfaces except for the drop panels.This is another reason why a flat slab is considered widely in office and commercial buildings.

• StructuralAccording to the calculations carried out in the appendix, the slab passes in long term and total deflection checks as specified by ACI 318-11. Also, the slab passes in minimum thickness specified by ACI 318-11. The original design of the slabs was carried out using the Indian Standard Code. Besides transferring gravity loads to columns, the slab also transfers lateral forces: wind and seismic to the central core shear walls. An advantage to structural engineer with this system is that it becomes to easy to tackle design changes that occur before and after the constriction started.

• ConstructionThe flat slab system is easy to construct by formwork and pouring of concrete. It is easy to find cheap labor to work on the constructed building. This system takes time because this time is consumed by the curing period. The formwork is readily available for rent or purchase by the construction personnel as there is ample of construction going on in the location.

Pros Cons

Low cost per square foot High seismic weightCheap labor available at construction site in India

Longer construction time

Provides an even ceiling except for the drop panel

Deflection becomes and issue as spans become longer

Provides good floor to ceiling height Drop panels are not preferred architecturally Vibration is not an issue



Composite Floor Slab system

In order to achieve spans as long as 27.6’ with minimum depth of the slab system, a composite system was selected as the first alternative to be tried in place of a flat slab. W10x22 beam was chosen to support 3” deep 3VLI concrete deck topped with 4” concrete to take the compression load from the steel. The decking runs perpendicular to the 10x22 beam. This beam is supported on W18x55 composite girder which is designed with the deck running parallel on it.

The beam is spaced at 9.2’ and spans 27.6’ long. The girder spans 27.6’ from one column to other. The beam sizes was controlled by live load deflections and design moments. Construction dead load was not used for design because it was assumed that shoring will be used while construction until the concrete reached at its maximum compressive strength. Shoring was considered as a cheaper option because shores and labor is cheaper instead of going for a larger beam depth that would compromise the floor to ceiling heights.



Fig. 10: Plan of Composite Flooring System

Fig. 11: 3VLI20 Metal Deck with concrete topping

Fig. 12: Cross Section of composite section W10x22

• GeneralThe 7.5 in total thickness (metal deck and topping) with wide flange beams weighs 81.4 psf which is lower as compared to the flat slab system. This system costs about $10 per square foot which is the cheapest of all the floor systems. The reason for this system to be cheaper is that minimum formwork and labor is used on construction. If we put this in the context of construction in India, the price will go higher because of the use of steel and steel manufacturing laborers for erection.

• ArchitectureAs the depth of the composite system increases by 10”, the floor to ceiling height also reduces. This height reduces in the area where the girder is located, in the area below beams the depth of system is 17.5” which is only 1 in greater as compared to flat slab system. The space within the floor system can be used to mechanical ductwork through co-ordination between structural engineer, mechanical engineer and architect. The architect can choose to expose the structure in the ceiling which is found in several office spaces in USA but not a lot in India.

• StructureThe live loads induce a deflection of 0.698 in which is close to the deflections in a flat slab and higher than deflection in a precast member. Due to reduction in overall weight of the floor system the foundation sizes can be reduced. However, the foundation also supports the lateral pressures from the soils and water table pressures from the ground. An in depth analysis will be required to balance the effect of load reduction on foundation and the soils pressures. Use of composite system will lead to change in the lateral system from concrete to steel frame. A steel braced or moment frame or a combination could be used as lateral force resisting system.

• ConstructionAs mentioned earlier, its assumed that labor force will be available for composite floor system. As shoring is considered, part of the job of labor force will be to install and dismantle the shoring. As the concrete topping is 4.5 in, the floor system has a fire rating of 2 hr.

Pros Cons

Lowers weight of the building Higher cost due to steel being expensive in India

Longer spans can be achieved Also, steel construction laborers are expensive in India

Structure can be exposed for a different architectural feel which can be unique for a building in India

Serviceability could be an issue

Less formwork required



Steel metal deck and Joist System

After looking into concrete and composite systems, the implications of a complete steel system was worth looking into. Using hand calculations, vulcraft deck catalog and steel joist institute catalog, a steel system design was carried out which consisted of steel metal decking topped with 2” concrete reinforced with welded wire fabric. The decking rested on long haul steel joists and a steel joist girder.

Live load deflections and superimposed dead loads were used to select the decking and joists. A 3 in deep 3C18 steel deck topped with 3in concrete was selected. A steel joist 18” deep 18LH09 was selected to support the decking and the joist was resting on 24” deep joist girder 24G7N18F. 7 18” joists supported the decking slab, 2 joists rested directly on the columns and 5 joists supported on 24” joist girder.

• GeneralThe steel metal deck and joist system is the lightest among all the floor systems and ranks 2nd from a cost perspective. This system costs $15.1 per square feet. Due to steel as a material and its accurate construction methods, the cost of construction would be higher in India. The



Fig. 13: Floor Plan of Steel decking, joists and joist girder

Fig. 14: 18C09 steel deck with 3” Concrete topping

depth of the system in the area were joist girder exits is 36” and the depth in the area of joist beams is 24”.

• ArchitectureThe change from a complete concrete to a steel system undergoes a lot of architectural changes. In order to adjust the floor-ceiling height, the overall height of the building need to be increased. Although this system has large depths, the ceiling can be used to run mechanical ductwork through the joists. This requires accurate co-ordination in the design team between and structural and mechanical engineer. Also, the columns spacing might need to be reduced to decrease the depth of the system.

• StructureA steel framed floor system requires steel columns and it goes through a significant load reduction as compared to concrete. Also, size reduction occurs in foundations after a balance is achieved between the soil bearing capacity, lateral earth pressures and the overall weight of the building. The lateral system will change to steel braced or moment frame or a combination. Converting to steel is one of the ways of making building greener as steel is a recyclable material and results in lighter building.

• ConstructionSteel construction is the fastest of the all three systems. However, it requires skilled labor onsite and construction precision which comes with a price.

Pros Cons

Very light as compared to comcrete systems Expensive due to steel and labor being expensive in India

Reduces foundation sizes Serviceability could be an issue Smaller column cross-sections will provide a better open floor plan

Columns spacing need to be reduced for higher floor to ceiling height

Steel can be recycled; promotes a sustainable building

Design change at the time of construction could be an issue due to pre-fabrication of steel Large system depth due to long spans



Precast Double Tee Floor System

The fastest way to achieve a building that is concrete is using a precast system. The concrete members are prefabricated in a factory in controlled conditions. The conditions in a manufacturing plant result in a members with higher quality. Prestressed double tee members are used which are 10 feet wide and 24 in deep. The double members are supported on prestressed inverted tee girders that carry the load to the columns.

The floor system is designed using the handbook of the Precast Concrete Institute (PCI) where members are selected using the service loads. As members are prestressed, long spans can be achieved.

General

The weight of a precast double tee is 74 psf which is the second lightest after steel metal deck system. It is the most expensive system at $17.6 per SF because, it also requires skilled laborers to lay the members on site and connect them to girders and columns. Also, transporting the large member is a concern. The depth of the girder is 36” and the depth of system at the double tee is 24”. The beams can be aligned in a way to allow space for mechanical ductwork and electrical wiring.

Architecture



Fig. 15: Plan of Precast slabs and inverted tee

Double Tee Slab

Double Tee Slab

Fig. 16: Precast Slab rendering detail

This system might not be a preference of the architects because of the maximum depth of the system - 36”. The only way to overcome this large depth is by increasing the overall height of the building. An architectural advantage of this system is using the long span capability and increasing the bay sizes, thus reducing the columns. This will help in achieving a more open floor plan which is desired in The Optimus.

Structure

The structural system acts like composite and flat slab system. The reduced weight will help reduction in foundations. In situation where there is no space for foundations and long spans occur, the prestressed precast system works perfectly. The lateral system will remain as concrete shear wall. Also, just like steel moment frame, a moment frame can be designing moment connections of precast members. The double tee and inverted tee members used are simplified as pin connections. They were checked for maximum live load deflection of 0.47 in.

Construction

The construction of precast system is similar to erecting a steel system. Precast members are transported from factory to construction site. They are placed using cranes. This precess eliminates the process of concrete curing. Hence, making it faster. One of the drawbacks is that that design changes after or during construction is difficult as members get casted in the plant. Hence, co-ordination among design teams is very important in constriction of a precast system.

Pros Cons

Efficient members can be manufactured by offsite curing of concrete

Transportation of members to site could be issue in tight spaces

Increases construction schedule High cost Difficult to modify after design is cone Reduces floor to ceiling height



Comparison table of Floor SystemsCriteriaCriteria

Two way flat plate with drop

panels(Existing system)

Composite Steel Metal deck with steel joists

Precast Double Tee with precast

inverted tee girder

General

Weight (psf) 98.5 81.4 58.5 74

GeneralCost ($/SF) 14.8 9.5 15.1 17.6

GeneralMaximum depth of system

16” at drop panels

25.5” to the base of the girder

30” to the base of the joist

girder36” to base of

girder

ArchitecturalBay size change N.A Not required

Lower bay size to increase floor

heightNot required

Architectural

Fire Rating 2 hr 2 hr 2 hr 2 hr

Structural

Impact on foundation

Existing Mat foundation

Size / Capacity can be reduced

Size / Capacity can be reduced

Size / Capacity can be

reduced

Structural

Impact on gravity system

Existing concrete columns

Steel or composite

columns can be used

Steel columns can be used

Concrete columns required

StructuralImpact on

lateral system

Concrete Shear wall

core Steel or concrete

option Steel braced

frame required Concrete shear

wall coreStructural

Maximum immediate deflection

0.670 in 0.698 in NA 0.47 in

Structural

Ease of post design

modification

Easy as concrete is

poured on site

Easy because concrete is used

by steel members are prefabricated

Difficult because

members are prefabricated

Difficult because

members are prefabricated

Construction

Impact on labor force

Does not require skilled

labor

Requires labor skilled in steel construction

Requires labor skilled in steel construction

Required labor skilled to erect prefabricated

concrete membersConstruction

Impact on schedule N.A

May reduce construction

schedule


schedule


schedule

Construction

Constructability Easy Medium Difficult Medium

FeasibilityFeasibility N/A Yes No Yes



ConclusionTechnical report 2 analyzed the existing floor system of The Optimus and compared it three alternative floor system design choices. A typical bay of office floor was selected to design and size the 3 floor systems. Common live loads and superimposed dead loads were used to size members based on moment capacity and deflections. The comparison in the systems was based on weight of the floor system, cost, constructability and impact on architecture and structure of the building. The intent was to achieve a system that balances out the three main characteristics to achieve an efficient system: weight, cost, floor to ceiling height.

The existing flat slab system is the heaviest of the four systems and the second least expensive. As there are a lot of contingencies involved in the loading, construction and design of the building in India, flat slab is one of the preferred system.

The composite system is the next most efficient system after flat slab because it is lighter and it ranks medium in terms of constructability as flat slab. The use of steel is the only factor that makes the system cost higher as compared to flat slab.

The third choice is a precast system that maximizes construction time, reduces labor and reduces weight. One significant limitation is that it has a large depth which lower floor to ceiling height.

A steel decking on joists is least considered system because it is expensive, it had large depth and constructability in the construction conditions in India would make it expensive.

A further in-depth analysis would help prove a more efficient system between flat slab and composite system.



Appendix 1: Flat Slab Punit G. Das | Structural Technical Report 2










Appendix 2: Composite Punit G. Das | Structural Technical Report 2














Appendix 3: Steel Metal Decking Punit G. Das | Structural Technical Report 2










MAXIMUM CONSTRUCTION CLEAR SPANS (S.D.I. CRITERIA)

REINFORCED CONCRETE SLAB ALLOWABLE LOADS

3 C CONFORM

NO

N-C

OM

PO

SIT

E

NOTES: 1. * As does not meet A.C.I. criterion for temperature and shrinkage.2. Recommended conform types are based upon S.D.I. criteria and normal weight concrete.3. Superimposed loads are based upon three span conditions and A.C.I. moment coefficients.4. Load values for single span and double spans are to be reduced.5. Vulcraft’s painted or galvanized form deck can be considered as permanent support in most building applications. See page 23.

If uncoated form deck is used, deduct the weight of the slab from the allowable superimposed uniform loads.6. Superimposed load values shown in bold type require that mesh be draped. See page 23.

34

Interlocking side lap is not drawn to show actual detail.

Appendix 4: Precast Floor System Punit G. Das | Structural Technical Report 2








Documents

Optimus - Penn State College of Engineering · IS Code Description IS 875 (Part 1): 1987 Dead loads IS 875 (Part 2): 1987 Imposed loads IS 875 (Part 3): 1987 Wind loads. 3))))) 1